LIDAR device

ABSTRACT

A LIDAR device includes a light source, a mirror, a rotatable shaft, and a motor. The light source configured to emit a light beam having a predetermined light beam width for scanning a scanning zone. The rotatable shaft has a center axis parallel to a reflective surface of the mirror and is connected to a back surface of the mirror. The motor is configured to rotate the shaft to cause the mirror to swing between a first position and a second position. The light source and the mirror are arranged to have a positional relationship such that a mirror center is aligned with the light beam center when the mirror is at the first position, and the mirror center shifts within a motion area when the mirror is swinging between the first position, non-inclusive, and the second position, inclusive.

TECHNICAL FIELD

The present disclosure relates to a LIDAR device to calculate a distanceto an object.

BACKGROUND ART

A LIDAR, which stands for Light Detection and Ranging, is a remotesensing method to measure distances to object in a scanning area. Such aLIDAR system has been well used in a variety of fields including in thefield of autonomous driving area. LIDAR system typically uses a lightemitter, a light receiver, and a mirror to reflect the emitted lighttoward the scanning area. The scanning mirror is usually used byrotating the mirror in one direction to scatter laser beams around asurrounding area.

SUMMARY

One aspect of the present disclosure is a LIDAR device for measuring adistance to an object in a scanning zone. The device includes a lightsource, a mirror, a rotatable shaft, and a motor. The light source isconfigured to emit a light beam having a predetermined light beam widthfor scanning the scanning zone. The mirror has a reflective surface anda back surface opposite to the reflective surface. The mirror isconfigured to reflect, with the reflective surface, the light beamemitted from the light source toward the scanning zone. The rotatableshaft has a center axis parallel to the reflective surface of themirror. The shaft is connected to the back surface of the mirror.

The motor is configured to rotate the shaft to cause the mirror to swingbetween a first position corresponding to one end of the predeterminedscanning zone and a second position corresponding to another end of thepredetermined scanning zone, an angle of incidence of the light beam tothe reflective surface being greater when the mirror is at the firstposition than when the mirror is at the second position.

When a light beam center is defined as a center of the light beam widthof the light beam from the light source to the reflective surface, thena motion area is defined as one side of the light beam center thatincludes the center axis of the shaft.

The light source and the mirror are arranged to have a positionalrelationship such that, when viewed in a direction along the center axisof the shaft, a mirror center, which is defined as a point on thereflective surface closest to the center axis of the shaft, is alignedwith the light beam center when the mirror is at the first position, andthe mirror center shifts within the motion area when the mirror isswinging between the first position, non-inclusive, and the secondposition, inclusive.

BRIEF DESCRIPTION OF DRAWINGS

The above and other objectives, features and advantages of the presentdisclosure will become more apparent from the following detaileddescription made with reference to the accompanying drawings.

FIG. 1 is a schematic view of a LIDAR device according to a firstembodiment.

FIG. 2 is a top view showing a positional relationship between aemitting module and a scanning mirror.

FIG. 3 is a side view of the LIDAR device.

FIG. 4 is a diagram showing the reflection of the laser beam by thescanning mirror at −60 deg. in (a), 0 deg. in (b), and +60 deg. in (c).

FIG. 5 is a block diagram of the LIDAR device.

FIG. 6 is a timing chart of detection signals, emission control signals,and return signals according to the first embodiment.

FIG. 7 is a flowchart performed by the LIDAR device according to thefirst embodiment.

FIG. 8 is a schematic view of a comparative example showing a positionalrelationship between the light emitting module and the scanning mirror.

FIG. 9 is a timing chart of a comparative example of detection signals,emission control signals, and return signals.

FIG. 10 is a timing chart of detection signals, emission controlsignals, and return signals according to a second embodiment.

FIG. 11 is a flowchart performed by the LIDAR device according to thesecond embodiment.

FIG. 12 is a timing chart of detection signals, emission controlsignals, and return signals according to a third embodiment.

FIG. 13 is a flowchart performed by the LIDAR device according to thethird embodiment.

FIG. 14 is a timing chart of detection signals, emission controlsignals, and return signals according to a fourth embodiment.

FIG. 15 is a flowchart performed by the LIDAR device according to thefourth embodiment.

FIG. 16 is a block diagram of the LIDAR device according to a fifthembodiment.

FIG. 17 is a timing chart of detection signals, emission controlsignals, and return signals according to the fifth embodiment.

FIG. 18 is a flowchart performed by the LIDAR device according to thefifth embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a plurality of embodiments of the present disclosure willbe described with reference to the drawings. In the followingembodiments, the same or equivalent parts are denoted by the samereference numerals as each other, and explanations will be provided tothe same reference numerals for simplifying descriptions. Furthermore,in the following embodiments, a laser imaging detection and ranging(LIDAR) device is mounted in a vehicle such as an automotive, but theLIDAR device 1 may be mounted in any kind of vehicles such asmotorbikes, airplanes, ships, drones, or the like.

First Embodiment

FIGS. 1 to 3 show a schematic view of the LIDAR device 10 according tothe first embodiment. The LIDAR device 10 is configured to calculate adistance to an object X in a scanning zone SZ using time-of-flight (ToF)techniques. The LIDAR device 10 basically includes a light emittingmodule 12, a light receiving module 14, a scanner module 18 (see FIG. 3), and a motor controller 50. Calculation of a distance to an object Xis performed by a controller 21 that is integrally disposed in the lightreceiving module 14, as will described later. It should be noted thatthe scanner module 18 is not illustrated in FIG. 1 for explanatorypurposes.

The LIDAR device 10 is formed as a single component housed in a box-likecase 10 a as illustrated in FIG. 1 . As shown in FIG. 3 , in thisembodiment, the light emitting module 12 and the light receiving module14 are arranged in a direction along a vertical direction (an up-downdirection) of a vehicle to which the LIDAR device 10 is mounted. Inother words, the light emitting module 12 and the light receiving module14 are arranged in a direction along rotatable shaft 24 of scannermodule 18. More specifically, the light emitting module 12 is disposedabove the light receiving module 14. However, the arrangement of thelight emitting module 12 and the light receiving module 14 is notnecessarily limited to this example. For example, the light emittingmodule 12 and the light receiving module 14 may be arranged in adirection along a horizontal or a slanted direction of the vehicle.

The light emitting module 12, or a light source, is configured to emit alaser light toward a scanning mirror 16 of the scanner module 18. Asshown in FIG. 2 , the light emitting module 12 includes two pairs oflight emitters 20 a, 20 b and transmitter lenses 22 a, 22 b. Each of thelight emitters 20 a, 20 b is, for example, a semiconductor laser diodeconfigured to emit a pulsed laser. Each of the light emitters 20 a, 20 bis electrically connected to the controller 21 and configured to emit alaser light when the light emitting module 12 receives an emissioncontrol signal from the controller 21. Therefore, the emission timing ofthe light emitters 20 a, 20 b are controllable through the emissioncontrol signals output from the controller 21.

The light emitting module 12 is further configured to output an actualemission timing to the controller 21. The actual emission timing is atiming at which the light emitting module 12 actually emits a lightbeam. As will described below, the actual emission timing is used forcompensating an error generated when calculating a distance by thecontroller 21.

Each of the transmitter lens 22 a, 22 b is a lens configured to focusthe pulsed laser emitted from the light emitter to form a vertical line(or a vertical band) extending in a direction along the verticaldirection of the vehicle (see FIG. 1 ). That is, the LIDAR device 10adopts the 1D line-scanning method which performs a horizontal scanningwith a vertical-line laser beam.

In this embodiment, the two pairs of the light emitters 20 a, 20 b andthe transmitter lenses 22 a, 22 b are arranged in the horizontaldirection. Hereinafter, a laser beam emitted from one (the left pair 20a, 22 a in FIG. 2 ) of the two pairs of the light emitters and thetransmitter lenses is referred to as a first laser beam, and a laserbeam emitted from the other one (the right pair 20 b, 22 b in FIG. 2 )of the two pairs of the light emitters and the transmitter lenses isreferred to as a second laser beam. Then, the first and second laserbeams emitted from the two light emitters 20 a, 20 b and focused throughthe transmitter lenses 22 a, 22 b are collectively referred to as alight beam band LB.

As shown in FIG. 2 , the light beam band LB of the two light emitters 20a, 20 b has a light beam width W which is a width in a directionperpendicular to a light travelling direction when viewed from above.Then, a light beam center BC is defined as a center of the light beamwidth W of the light beam band LB. More specifically, the light beamcenter BC is a center line extending along center points of the lightbeam width W in a direction perpendicular to the light travellingdirection when viewed above.

The scanner module 18 includes the scanning mirror 16, a rotatable shaft24, a driving motor 26, and an angle sensor 28. The rotatable shaft 24is a shaft configured to rotate about a center axis CX. In thisembodiment, the center axis CX extends along a direction in parallelwith the vertical direction of the vehicle. The rotatable shaft 24 has acolumnar shape with a specified diameter. The side surface 24 a of therotatable shaft 24 is connected to the mirror 16.

The scanning mirror 16 is a mirror configured to reflect the laser beamtoward the scanning zone SZ directly or indirectly through another oneor more mirror. Furthermore, the scanning mirror 16 in this embodimentis configured to reflect the return beam reflected by an object X towardthe light receiving module 14. That is, the scanning mirror 16 serve asboth a transmitter mirror and a receiver mirror.

The scanning mirror 16 is a plate-like member in this embodiment andincludes a reflective surface 16 a and a back surface 16 b that isopposite to the reflective surface 16 a. The back surface 16 b of thescanning mirror 16 is connected to the side surface of the rotatableshaft 24. Thus, as shown in FIG. 2 , the reflective surface 16 a is awayfrom the center axis CX of the rotatable shaft 24 with a predetermineddistance (i.e., the radius of the rotatable shaft 24), and as a result,the scanning mirror 16 is rotated around, not about, the center axis CX(i.e., swinging).

In this embodiment, the reflective surface 16 a has a rectangular shapewhen viewed from the front (see FIG. 5 ). The reflective surface 16 a iselongated in a direction along the vertical direction. Referring to FIG.5 , two edge portions 30 of the reflective surface 16 a are defined asportions that include elongated sides (i.e., the lengths of thereflective surface 16 a) of the reflective surface 16 a extending in thedirection along the vertical direction. Also, a center portion 32 of thereflective surface 16 a is defined as a portion that is an center areaof the reflective surface 16 a between the two edge portions 30. Then, amirror center MC is defined as a point on the reflective surface 16 a,when viewed in a direction along the center axis CX (i.e., the verticaldirection), that is closest to the center axis CX of the rotatable shaft24, as shown in FIG. 2 . In this embodiment, the mirror center MC is acenter point between the two edge portions 30 when viewed in thedirection along the center axis CX. In other words, the mirror center MCis a center point of the width of the reflective surface 16 a.

The driving motor 26 is an electric motor configured to rotate therotatable shaft 24 about the center axis CX. The driving motor 26 iselectrically connected to the motor controller 50 and the operation ofthe driving motor 26 is controlled by motor driving signals output fromthe motor controller 50. The motor controller 50 is, for example, anelectronic control unit (ECU) that includes at least one processor andone memory. The memory includes random access memory, read only memory,flash memory, or a combination of these. The memory has stored thereoninstructions which, when executed by the processor, cause the processorto control the driving motor 26.

The motor controller 50 is configured to control the driving motor 26 tooperate alternately in opposite directions. As a result, the rotatableshaft 24 is rotated by the motor back and forth so that the scanningmirror 16 swings between a first position and a second position in apredetermined scanning angle range. That is, the scanning mirror 16periodically swings between the first position and the second position.

As shown in FIG. 2 , the first position of the scanning mirror 16 is aposition corresponding to one end A of the scanning zone SZ and thesecond position of the scanning mirror 16 is the other end B of thescanning zone SZ. As shown in FIG. 4 , an angle of incidence of thelight beam to the reflective surface 16 a is greater when the mirror isat the first position than when the mirror 16 is at the second position.In this embodiment, the scanning angle range is set to 120 degrees(i.e., −60°≤scanning angle θ≤+60°, and the scanning angle θ is −60° whenthe scanning mirror 16 is at the first position and the scanning angle θis +60° when the scanning mirror 16 is at the second position (see FIG.4 ).

Referring to FIG. 2 , a motion area is defined as one side of the lightbeam center BC that includes the center axis CX of the shaft 24 whenviewed in a direction along the center axis CX (the hatched area in FIG.2 ). Then, the light emitting module 12 and the scanning mirror 16 arearranged to have a positional relationship such that, when viewed in adirection along the center axis CX of the rotatable shaft 24, the mirrorcenter MC is aligned with the light beam center BC when the mirror is atthe first position (see FIG. 2 and (a) of FIG. 4 ). On the other hand,the mirror center MC shifts within the motion area when the mirror 16 isswinging between the first position, non-inclusive, and the secondposition, inclusive (see (b) and (c) in FIG. 4 ). In other words, themirror center MC of the scanning mirror 16 moves within the motion areaexcept when the scanning mirror 16 reaches the first position. Thus, themirror center MC and the light beam center BC are offset from each otherexcept when the mirror 16 is at the first position.

As shown in (a) of FIG. 4 , when the scanning mirror 16 is at the firstposition, the first laser beam emitted from the left light emitter isreflected at the left edge portion 30 of the reflective surface 16 a andthe second laser beam emitted from the right light emitters is reflectedat the right edge portion 30 of the reflective surface 16 a. On theother hand, as shown in (c) of FIG. 4 , when the scanning mirror 16 isat the second position, the first and second laser beams emitted fromboth the light emitters are reflected at the center portion 32 of thereflective surface 16 a.

The scanner module 18 further includes the angle sensor 28 that detectsrotation angles of the scanning mirror 16. The angle sensor 28 may be anoptical sensor, a mechanical sensor, an ultrasonic sensor, or the like.The angle sensor 28 is configured to detect a rotation angle at aplurality of predetermined angle intervals during each rotation cycle ofthe scanning mirror 16 between the first position and the secondposition. In this embodiment, the angle sensor 28 is configured todetect each 0.1 degree of the rotation angle of the mirror 16 (i.e., themaximum angle resolution is 0.1°). However, the resolution of the anglesensor 28 is not necessarily limited to 0.1 degree, and may be 0.05 or0.2 degree, for example.

The angle sensor 28 is connected to the controller 21 and is configuredto output a detection signal indicative of the rotation angle of themirror at the angle intervals (i.e., at 0.1 degree intervals). Inventorsof the present disclosure have found that since the scanning mirror 16is moved to swing between the first position and the second position, anacceleration is applied to the scanning mirror 16 during swinging.Therefore, the rotational speed of the scanning mirror 16 varies (doesnot maintain a constant value) during one rotation cycle of the scanningmirror 16. As a result, the rotation angle of the scanning mirror 16 isnot counted by the angle sensor 28 at same time intervals, as shown inFIG. 6 . That is, the angle sensor 28 outputs a detection signal at thesame angle intervals, but different time intervals, to the controller21.

The light receiving module 14 includes a light receiver 34 and thecontroller 21. The light receiver 34 includes an integrated circuit 36having a plurality of light sensitive devices, and the controller 21 isprovided within the integrated circuit 36 of the light receiver 34. Inother words, the light receiver 34 and the controller 21 are integrallyformed as a single module in this embodiment. In this embodiment, theplurality of light sensitive devices of the light receiver 34 are singlephoton avalanche diodes (SPADs) 38 which are formed as a 2-D SPAD array34 a by arranging the plurality of SPADs 38 in both columns and rows.Since the SPAD array 34 a constitutes a digital circuit and thereforehas a high angular resolution as compared with other light sensitivedevices forming an analog type circuit. Hence, the light receiver 34 candetect a return beam at small rotation angle intervals such as 0.1degree intervals. The light receiver 34 (the SPAD array 34 a) outputs areturn signal, which is a digital signal, in accordance with a returnbeam reflected by an object X to the controller 21 upon receiving thereturn beam. The light receiver 34 also includes a decoder 40 that isconfigured to enable diodes 38 in a column to receive a return beam.

The controller 21 in this embodiment is configured to control emissionof laser beams by controlling the light emitting module 12. Thecontroller 21 is further configured to calculate a distance to an objectX based on the difference between the light emission timing at which thelight emitting module 12 emitted a laser beam and the light receipttiming at which the light receiving module 14 received a return beam, aswill described later. Since the controller 21 is implemented on theintegrated circuit 36, which is a digital circuit, together with thelight receiver 34 (the SPAD array 34 a), the controller 21 is capable ofperforming the above-mentioned functions without a programmableprocessor.

FIG. 5 shows functional blocks of the controller 21. Although FIG. 5shows the controller 21 having these functions, one or some of functionsmay be executed by one or more physically separated circuit. Thecontroller 21 includes, as functional blocks, an emission controlsection 39 and a calculating section 40.

The emission control section 39 is configured to control the lightemitting module 12 by outputting an emission control signal to the lightemitting module 12. In this embodiment, the emission control section 39is configured to output an emission control signal upon receiving adetection signal from the angle sensor 28 (see FIG. 6 ). Thus, the lightemitting module 12 emits a laser beam each time the angle sensor 28detects a rotation angle of the scanning mirror 16. In other words, thelight emitting module 12 emits a laser beam at the same intervals as theangle intervals (i.e., 0.1 degree intervals). Furthermore, the emissioncontrol section 39 is configured to output a signal output timing to thecalculating section 40. The signal output timing is a timing at whichthe emission control section 39 output the control signal to the lightemitting module 12.

The calculating section 40 is configured to calculate a distance to anobject X using the return signal from the light receiving module 14 andthe signal output timing from the emission control section 39. Morespecifically, the calculating section 40 calculates a distance to anobject X from the time difference between the signal output timing andthe light receipt timing (i.e., the return signal) using thetime-of-flight principle. Furthermore, the calculating section 40 isconfigured to receive the above-described actual emission timing fromthe light emitting module 12 (see FIG. 5 ). Then, the calculatingsection 40 is configured to correct the calculated distance using theactual emission timing. That is, there is a time lag after thecontroller 21 outputs the signal output timing until the light emittingmodule 12 actually emits a laser beam. Therefore, the controller 21corrects the distance calculated from the signal output timing using theactual emission timing.

FIG. 7 shows a flowchart executed by the LIDAR device 10 to calculate adistance to an object X. When the angle sensor 28 detects a rotationangle of the scanning mirror 16 at step S10, the angle sensor 28 outputsa detection signal indicative of the detected rotation angle to thecontroller 21 (the emission control section 39) at step S20. Asdescribed above, the angle sensor 28 detects a rotation angle at thepredetermined rotation angle intervals (i.e., 0.1 degree intervals)although the rotational speed of the scanning mirror 16 varies betweenthe first position and the second position. When the controller 21receives the detection signal from the angle sensor 28, the controller21 outputs an emission control signal to the light emitting module 12 atstep S30.

When the light emitting module 12 receives the emission control signal,the light emitting module 12 emits a laser beam toward the scanningmirror 16 at step S40. The light emitting module 12 further outputs theactual emission timing to the controller 21 (the calculating section 40)at step S50 as a timing at which the light emitting module 12 actuallyemits the laser timing.

The emitted laser beam is reflected at the reflective surface 16 a ofthe scanning mirror 16 and travels to the scanning zone SZ. Then, if thelaser beam is reflected by an object X, the return signal comes back tothe LIDAR device 10 and is reflected again by the reflective surface 16a of the scanning mirror 16 toward the light receiving module 14. Whenthe return beam reaches the light receiving module 14, the lightreceiving module 14 (the SPAD array) detects the return beam at stepS60, and then the light receiving module 14 outputs a return signal tothe controller 21 (the calculating section 40) in response to receivingthe return beam at step S70.

The controller 21 (the calculating section 40) calculates a distance tothe object X using the signal output timing and the return signal atstep S80. Then, the controller 21 (the calculating section 40) correctsthe calculated distance using the actual emission timing at step S90.

As described above, the LIDAR device 10 according to the firstembodiment includes the light emitting module 12 and the scanning mirror16 that are arranged to have a positional relationship such that, whenviewed in a direction along the center axis CX of the rotatable shaft24, the mirror center MC is aligned with the light beam center BC whenthe mirror 16 is at the first position. The first position is defined asa position corresponding to the one end A of the scanning zone SZ, andthe angle of incidence of the light beam to the reflective surface 16 ahas a maximum value in the scanning angle range when the scanning mirror16 is at the first position. On the other hand, the mirror center MCshifts within the motion area when the mirror 16 is swinging between thefirst position, non-inclusive, and the second position, inclusive. Thesecond position is defined as a position corresponding to the other endB of the scanning zone SZ, and the angle of incidence of the light beamto the reflective surface 16 a has a minimum value in the scanning anglerange when the scanning mirror 16 is at the second position.

Thus, since the light beam center BC is aligned with the mirror centerMC when the scanning mirror 16 is at the first position, the first lightbeam and the second light beam are reflected at the edge portions 30 ofthe reflective surface 16 a between which the mirror center MC islocated. More specifically, as shown in (a) of FIG. 4 , the first lightbeam and the second light beam are reflected at the left edge portionand the right edge portion of the reflective surface 16 a, respectively,when the scanning mirror 16 is at the first position. Therefore, thewidth of the reflective surface 16 a (the scanning mirror 16) can beminimized as long as the reflective surface 16 a can receive the firstand second light beams at the both edge portions 30 when the mirror 16is at the first position. As a result, the size of the LIDAR device 10can be reduced because of the mirror 16 with a minimum width.

On the contrary, if the light emitting module 12 and the scanning mirror16 are arranged so that the mirror center MC is aligned with the centeraxis CX as illustrated in FIG. 8 , at least the left side of thereflective surface 16 a needs to be extended so as to catch the firstlaser beam when the scanning mirror 16 is at the first position. As aresult, the size of the LIDAR device 10 would be increased because ofthe mirror 16 with an extended width.

In this embodiment, the angle sensor 28 is disposed to detect rotationangles of the scanning mirror 16 and outputs a detection signal at aplurality of predetermined angle intervals (0.1 degree intervals in thisembodiment) during each rotation cycle between the first position andthe second position of the scanning mirror 16. Then, the controller 21outputs a control signal to the light emitting module 12 upon receivingthe detection signal from the angle sensor 28, as shown in FIG. 6 . As aresult, the light emitting module 12 can emit a laser beam at the sameintervals as the plurality of predetermined angle intervals.

Here, FIG. 9 shows a comparative example where the light emitting module12 is controlled to emit a laser beam at a plurality of predetermined“time” intervals (for example, each 27.8 microseconds). Since thescanning mirror 16 swings between the first and second positions, therotational speed irregularly varies due to an acceleration applied tothe mirror 16. Thus, although the light emitting module 12 can emit alaser beam at a predetermined “time” intervals, the light emittingmodule 12 cannot emit a laser beam at a plurality of predetermined“rotation angle” intervals between the first and second positions. As aresult, the amount of laser beams would vary for each region of thescanning zone SZ corresponding to each of the rotational angleintervals.

On the contrary, since the light emitting module 12 is controlled toemit laser beams based on rotation angles, not time intervals, of thescanning mirror 16 detected by the angle sensor 28 according to thisembodiment, the LIDAR device 10 can emit a laser beam evenly for eachrotational angle interval. Thus, the LIDAR device 10 can scan thescanning zone SZ equally.

The light receiving module 14 includes the integrated circuit 36 onwhich the controller 21 is implemented. That is, the controller 21 isintegrally formed with the light receiver 34 (the SPAD array 34 a) inthis embodiment, and the distance between the controller 21 and thelight receiver 34 can be reduced as compared with a situation where thecontroller 21 is physically separated away from the light receiver 34.As a result, a required time for transmitting the return signal to thecontroller 21 from the light receiver 34 can be reduced, and thereforeaccuracy of the calculated distance can be increased.

The light receiving module 14 includes the plurality of SPADs 38 aslight sensitive devices. The SPADs 38 have a sensitivity to receive areturn beam with high resolution time intervals. Therefore, the lightreceiving module 14 can detect a return beam even at small rotationangle intervals (i.e., 0.1 degree in this embodiment), and thus theLIDAR device 10 can finely scan the scanning zone SZ. Furthermore, theSPAD array forms a digital circuit together with the controller 21.Thus, the distance to an object X can be calculated without a processor,which results in reduction of a manufacturing cost of the LIDAR device10.

In this embodiment, the light emitting module 12 is configured to outputthe actual emission timing at which the light emitting module 12actually emits the light beam. Then, the controller 21 corrects thecalculated distance using the actual emission timing. Thus, although thedistance is calculated using the signal output timing at which thecontroller 21 output the control signal to the light emitting module 12,and therefore the calculated distance inevitably includes an errorgenerated from the time lag between the signal output timing and theactual emission timing, the error can be corrected, or compensated,using the actual emission timing. As a result, the LIDAR device 10 canobtain a distance to an object X with high accuracy.

Second Embodiment

Next, the second embodiment of the present disclosure is described withreference to FIGS. 10 to 11 . In the following description, onlydifferent portions from the first embodiment will be described.

In the first embodiment, the controller 21 is configured to output anemission control signal upon receiving a detection signal from the anglesensor 28. In the second embodiment, the controller 21 is configured to,upon receiving the detection signal from the angle sensor 28, output aplurality of control signals to the light emitting module 12 prior toreceiving a subsequent one of the detection signal.

More specifically, as shown in FIG. 10 , the controller 21 outputs apredetermined number of control signals within each rotational angleinterval (i.e., between when the controller 21 receives a detectionsignal and when the controller 21 receives a subsequent detectionsignal). In this embodiment, the number of the control signals outputwithin each rotation angle interval is 10. Furthermore, the controller21 continuously outputs a control signal at predetermined “time”intervals (not rotational angle intervals) ten times and then stopsoutputting the control signal when the tenth control signal isoutputted.

The controller 21 is further configured to calculate a distance to anobject X using a plurality of return signals corresponding to theplurality of control signals for each rotational angle interval. Forexample, the controller 21 calculates ten distances corresponding to theten control signals for each rotation angle interval. Then, thecontroller 21 accumulates the ten distances and obtains an averagedistance from the ten calculated distances.

FIG. 11 shows a flowchart of a process performed by the LIDAR device 10according to the second embodiment. It should be noted that steps forcorrecting the calculated distance using the actual emission timing(i.e., steps S50 and S90 in FIG. 7 ) are eliminated in the secondembodiment.

When the angle sensor 28 detects a rotation angle of the scanning mirror16 at step S100, the angle sensor 28 outputs a detection signalindicative of the detected rotation angle to the controller 21 at stepS110. When the controller 21 receives the detection signal from theangle sensor 28, the controller 21 outputs an emission control signal tothe light emitting module 12 at step S120.

When the light emitting module 12 receives the emission control signal,the light emitting module 12 emits a laser beam toward the scanningmirror 16 at step S130. The emitted laser beam is reflected at thereflected surface of the scanning mirror 16 and travels to the scanningzone SZ. Then, if the laser beam is reflected by an object X, the returnbeam comes back to the LDIAR device and is reflected again by thereflective surface 16 a of the scanning mirror 16 toward the lightreceiving module 14. When the return beam reaches the light receivingmodule 14, the light receiving module 14 detects the return beam at stepS140, and then the light receiving module 14 outputs a return signal tothe controller 21 at step S150 in response to receiving the return beam.

The controller 21 calculates a distance to the object X using the signaloutput timing and the return signal at step S160. Then, the controller21 determines whether the number of the emission control signals emittedafter receiving the detection signal is ten at step S170. If the numberis not ten (step S170: No), the process proceeds to step S180, and thecontroller 21 determines whether a predetermined time interval (forexample, 3 microseconds) has elapsed after outputting the emissioncontrol signal. If the time interval has not elapsed (step S180: No),the controller 21 repeats step S180. If the time interval has elapsed(step S180: Yes), the process proceeds to step S120 and the controller21 outputs again an emission control signal. Then, the process repeatssteps S120 to S160, and the controller 21 determines whether the numberof the emitted emission control signals is ten. If Yes at step S170, thecontroller 21 stops outputting an emission control signal at step S190,and then calculates an average distance from the ten calculateddistances at step S200. Then, the process returns to step S100.

As described above, the LIDAR device 10 according to the secondembodiment outputs a plurality of emission control signals uponreceiving a detection signal from the angle sensor 28 until receiving asubsequent detection signal. Then, the controller 21 calculates aplurality of distances to an object X based on a plurality of returnsignals corresponding to the plurality of emission control signals, andobtains an average distance from the plurality of calculated distances.Therefore, the LIDAR device 10 can obtain a distance to an object X withhigh accuracy.

Third Embodiment

Next, the third embodiment of the present disclosure is described withreference to FIGS. 12 to 13 . In the following description, onlydifferent portions from the first and second embodiments are described.

In the second embodiment, the controller 21 is configured to output apredetermined number (for example, ten) of emission control signalsafter receiving a detection signal until receiving a subsequentdetection signal. In the third embodiment, the controller 21 isconfigured to continuously output emission control signals atpredetermined time intervals after receiving a detection signal untilreceiving a subsequent detection signal (see FIG. 14 ).

As with the second embodiment, the controller 21 calculates a pluralityof distances to an object X for each rotation angle interval based on aplurality of return signals corresponding to the plurality of emissioncontrol signals, and then obtains an average distance from the pluralityof calculated distances.

FIG. 13 shows a flowchart of a process performed by the LIDAR device 10according to the second embodiment. It should be noted that, as with thesecond embodiment, steps for correcting the calculated distance usingthe actual emission timing (i.e., steps S50 and S90 in FIG. 7 ) areeliminated in the third embodiment.

When the angle sensor 28 detects a rotation angle of the scanning mirror16 at step S300, the angle sensor 28 outputs a detection signalindicative of the detected rotation angle to the controller 21 at stepS310. When the controller 21 receives the detection signal from theangle sensor 28, the controller 21 outputs an emission control signal tothe light emitting module 12 at step S320. When the light emittingmodule 12 receives the emission control signal, the light emittingmodule 12 emits a laser beam toward the scanning mirror 16 at step S330.

When the return beam reaches the light receiving module 14, the lightreceiving module 14 detects the return beam at step S340, and then thelight receiving module 14 outputs a return signal to the controller 21in response to receiving the return beam at step S350.

The controller 21 calculates a distance to the object X using the signaloutput timing and the return signal at step S360. Then, the controller21 determines whether the controller 21 receives a subsequent detectionsignal from the angle sensor 28 after receiving the previous detectionsignal at S370. If step S370 is No, the process proceeds to step S380,and then the controller 21 determines whether a predetermined timeinterval (for example, 3 microseconds) has elapsed after outputting theemission control signal. If the time interval has not elapsed (stepS380: No), the controller 21 repeats step S380. If the time interval haselapsed (step S380: Yes), the process returns to step S320 and thecontroller 21 outputs again an emission control signal. Then, theprocess repeats steps S320 to S370, and the controller 21 output aplurality of emission control signals at the predetermined timeintervals until receiving the subsequent detection signal.

If the controller 21 determines that the controller 21 receives thesubsequent detection signal from the angle sensor 28 (step S370: Yes),the controller 21 calculates an average distance from the plurality ofcalculated distances at step S380. Then, the process returns to stepS320, and the controller 21 outputs again a plurality of emissioncontrol signals at the predetermined time intervals by repeating stepsS320 to S370.

As described above, the LIDAR device 10 according to the thirdembodiment continuously outputs a plurality of emission control signalsat predetermined time intervals for each rotation angle interval. Then,the controller 21 calculates a plurality of distances to an object X foreach rotation angle interval based on a plurality of return signalscorresponding to the plurality of emission control signals, and obtainsan average distance from the plurality of calculated distances.Therefore, as with the second embodiment, the LIDAR device 10 can obtainthe distance to an object X with high accuracy.

Fourth Embodiment

Next, the fourth embodiment of the present disclosure is described withreference to FIGS. 14 to 15 . In the following description, onlydifferent portions from the first to third embodiments are described.

In the first embodiment, the controller 21 is configured toautomatically output an emission control signal upon receiving adetection signal from the angle sensor 28. In the fourth embodiment, thecontroller 21 is configured to output an emission control signal if thedetection signal (the rotation angle) matches any one of a plurality oftarget rotation angles (see FIG. 14 ). In this embodiment, the targetrotation angles are set to 0.0, 0.2, 0.4, 0.6, . . . , 120.00 degree,for example.

FIG. 15 shows a flowchart of a process performed by the LIDAR device 10according to the fourth embodiment. It should be noted that steps forcorrecting the calculated distance using the actual emission timing(i.e., steps S50 and S90 in FIG. 7 ) are eliminated in the fourthembodiment.

When the angle sensor 28 detects a rotation angle of the scanning mirror16 at step S400, the angle sensor 28 outputs a detection signalindicative of the detected rotation angle to the controller 21 at stepS410. When the controller 21 receives the detection signal from theangle sensor 28, the controller 21 determines whether the detectionsignal matches any one of the target rotation angles at step S420. If Noat step S420, the process returns to step S400 and repeats steps S410 toS420. If Yes at step S420, the controller 21 outputs an emission controlsignal to the light emitting module 12 at step S430.

When the light emitting module 12 receives the emission control signal,the light emitting module 12 emits a laser beam toward the scanningmirror 16 at step S440. Accordingly, the LI DAR device 10 can emit alaser beam when the scanning mirror 16 is at a desired rotation angle.When the return beam reaches the light receiving module 14, the lightreceiving module 14 detects the return beam at step S450, and then thelight receiving module 14 outputs a return signal to the controller 21in response to receiving the return beam at step S460.

The controller 21 calculates a distance to the object X using the signaloutput timing and the return signal at step S470. Then, the processreturns to step S400 and repeats steps S410 to S470.

As described above, the LIDAR device 10 according to the fourthembodiment outputs an emission control signal when the rotation anglematches any one of the plurality of target rotation angles. Thus, theLIDAR can emit a laser beam toward a desired area in the scanning zoneSZ accurately.

In the above-described fourth embodiment, the target rotational anglesare set in a regular manner (e.g., 0.0, 0.2, 0.4, etc.). However, thetarget rotational angles may be set in an irregular manner using, forexample, a predetermined target angle table stored in at least onememory. In such a case, at least one processor may be used to determinewhether the detection signal (the rotational angle) matches a targetrotation angle.

Fifth Embodiment

Next, the fourth embodiment of the present disclosure is described withreference to FIGS. 16 to 18 . In the following description, onlydifferent portions from the first to fourth embodiments are described.In the above-described embodiments, the LIDAR device 10 emits a laserlight in a constant manner for each rotation angle interval (forexample, one laser beam is emitted for each rotation angle in the firstembodiment and a plurality of laser beams are emitted for each rotationangle in the second and third embodiments). In the fifth embodiment, theLIDAR device 10 is configured to emit a laser beam in a different mannerfor a specific target area within the scanning zone SZ the remainingarea.

In this embodiment, a specific rotation angle range of the scanningmirror 16 corresponding to the target area is defined in the rotationangle range (for example, −20°≤specific rotation angle θs≤+20°). Asshown in FIG. 17 , the light emitting module 12 is configured to emit alaser beam in a different manner within the rotational angle range thanthe other rotational angle range (i.e., −60°≤θ<−20° and +20°<θ≤+60). Forexample, the light emitting module 12 is controlled to emit apredetermined number of laser beams (e.g., 10) for each rotational angleinterval within the specific rotation angle range. Hereinafter, therotation angle range of the scanning mirror 16 other than the specificrotation angle range is referred to as a regular range within which thelight emitting module 12 is controlled to emit a laser beam uponreceiving the detection signal from the angle sensor 28 as with thefirst embodiment.

In this embodiment, the controller 21 is separately provided with thelight receiving module 14 as shown in FIG. 16 . That is, the lightreceiving module 14 does not integrally include the controller 21 asdescribed in the first embodiment. The controller 21 is an electroniccontrol unit (ECU) that includes at least one processor 21 a and atleast one memory 21 b instead of, or in combination of, at least onecircuit in this embodiment. The memory 21 b includes random accessmemory, read only memory, flash memory, or a combination of these. Thememory 21 b has stored thereon instructions which, when executed by theprocessor 21 a, cause the processor 21 a to perform a variety of tasksas will be described later. The memory 21 b also has stores the specificrotational angle range.

FIG. 18 shows a flowchart executed by the LIDAR device 10 according tothis embodiment. It should be noted that steps for correcting thecalculated distance using the actual emission timing (i.e., steps S50and S90 in FIG. 7 ) are eliminated in the second embodiment.

When the angle sensor 28 detects a rotation angle of the scanning mirror16 at step S500, the angle sensor 28 outputs a detection signal at stepS510. When the controller 21 receives the detection signal from theangle sensor 28, the controller 21 (the processor 21 a) determineswhether the rotation angle of the scanning mirror 16 is within thespecific rotation angle range at step S520. If No at step S520 (therotation angle is within the regular range), the process proceeds tostep S530, and the controller 21 outputs an emission control signal.Accordingly, the controller 21 outputs an emission control signal uponreceiving the detection signal when the rotation angle of the scanningmirror 16 is within the regular angle.

When the light emitting module 12 receives the emission control signal,the light emitting module 12 emits a laser beam toward the scanningmirror 16 at step S540. Then, when the return beam reaches the lightreceiving module 14, the light receiving module 14 detects the returnbeam at step S550, and then the light receiving module 14 outputs areturn signal to the controller 21 at step S560 in response to receivingthe return beam.

The controller 21 calculates a distance to an object X using the signaloutput timing and the return signal at step S570. Then the processreturns to step S500. In this way, when the rotation angle is within theregular range, a distance to the object X is calculated for eachrotation angle interval.

If the controller 21 determines that the rotation angle is within thespecific rotation angle range at step S520 (step S520: Yes), the processproceeds to step S580, and then the controller 21 outputs an emissioncontrol signal at step S580. When the light emitting module 12 receivesthe emission control signal, the light emitting module 12 emits a laserbeam toward the scanning mirror 16 at step S590. Then, when the returnbeam reaches the light receiving module 14, the light receiving module14 detects the return beam at step S600, and then the light receivingmodule 14 outputs a return signal to the controller 21 at step S610 inresponse to receiving the return beam.

If the controller 21 receives the return signal, the controller 21calculates a distance to the object X using the return signal at stepS620. Then, the controller 21 determines whether the number of emissionof the emission control signal after receiving the detection signal isten at step S630. If No at step S630, the process proceeds to step S640,and the controller 21 determines whether a predetermined time interval(for example, 3 microseconds) has elapsed after outputting the emissioncontrol signal. If the time interval has not elapsed (step S640: No),the controller 21 repeats step S640. If the time interval has elapsed(step S640: Yes), the process proceeds to step S580 and the controller21 outputs again an emission control signal. Then, the process repeatssteps S590 to S620, and the controller 21 determines whether the numberof the emitted emission control signals is ten at S630. If Yes at stepS630, the controller 21 stops outputting an emission control signal atstep S650, and then calculates an average distance from the tencalculated distances at step S660. Then, the process returns to stepS500.

Accordingly, when the rotation angle is within the specific rotationangle range, the controller 21 outputs ten emission control signals foreach rotation angle interval. The controller 21 calculates ten distancesbased on ten return signals corresponding to the ten emission controlsignals. Then, the controller 21 obtains an average distance from theten calculated distances for each rotation angle interval within thespecific rotation angle range. Therefore, the LIDAR device 10 accordingto the fifth embodiment can finely scan a specific area of the scanningzone SZ and obtain a distance to an object X with high accuracy for sucha specific area.

Modifications to Embodiments

Several modifications may be applied to the above-described embodiments.

For example, in the embodiments described above, the light emittingmodule is configured to emit two laser beams from two light emittingelements. However, the light emitting module may emit a laser beam froma single light emitting element or three or more laser beams from threeor more light elements.

In the above-described embodiments, the light emitting module isconfigured to emit laser light during the entire cycle of the scanningmirror (i.e., one way from the first positon to the second position andthe other way from the second position to the first position). However,the light emitting module may be configured to emit laser light duringonly one way of the scanning mirror. For example, the light emittingmodule may be controlled to emit laser lights only when the mirror isswinging from the first position to the second position. In this case,the mirror is quickly returned back to the first position immediatelyafter the mirror moved to the second position.

In the above-described embodiments, the light receiver includes aplurality of SPADs. However, other light sensitive elements may be used.However, if SPADs are used as a light receiver, since the SPADs canoutput a digital signal, there is no need to use a processor tocalculate a distance to an object as described above.

In this application, the terms “module” and “system” may includehardware components such as housings, fixtures, wiring, etc. Inaddition, in this application, the term “processor” may refer to, bepart of, or include circuits or circuitry that may include processingcore hardware (shared, dedicated, or group) that executes code andmemory hardware (shared, dedicated, or group) that stores code executedby the processing core hardware. As such, the term “processor” may bereplaced by the term “circuit”.

The method steps, processes, and operations described herein are not tobe construed as necessarily requiring their performance in theparticular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

Although the terms “first”, “second”, “particular”, etc. are be used todescribe various elements, these terms may be only used to distinguishone element from another. Terms such as “first,” “second,” and othernumerical terms when used herein do not imply a sequence or order unlessclearly indicated by the context. Thus, a first element, component,region, layer or section discussed below could be termed a secondelement, component, region, layer or section without departing from theteachings of the example embodiments.

Spatially relative terms, such as “front”, “rear,” “left”, “right”, andthe like, may be used for ease of description to describe one element orfeature's relationship to another element(s) or feature(s) asillustrated in the figures. Spatially relative terms may be intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if thesensor system in the figures is rotated, elements described as“front/rear” would then be oriented “left/right” with respect to thevehicle. Thus, the example term “front” can encompass any direction inpractice. The device may be otherwise oriented (rotated 90 degrees or atother orientations) and the spatially relative descriptors used hereininterpreted accordingly.

The invention claimed is:
 1. A LIDAR device for measuring a distance to an object in a predetermined scanning zone, the device comprising: a light source configured to emit a light beam having a predetermined light beam width for scanning the scanning zone, the light beam including at least a first light beam and a second light beam; a mirror that has a reflective surface and a back surface opposite to the reflective surface, the mirror configured to reflect, with the reflective surface, the light beam emitted from the light source toward the scanning zone; a rotatable shaft having a center axis parallel to the reflective surface of the mirror, the shaft being connected to the back surface of the mirror; and a motor configured to rotate the shaft to cause the mirror to swing between a first position corresponding to one end of the predetermined scanning zone and a second position corresponding to another end of the predetermined scanning zone, an angle of incidence of the light beam to the reflective surface being greater when the mirror is at the first position than when the mirror is at the second position, wherein: when a light beam center is defined as a center of the light beam width of the light beam from the light source to the reflective surface, then a motion area is defined as one side of the light beam center that includes the center axis of the shaft, the light source and the mirror are arranged to have a positional relationship such that, when viewed in a direction along the center axis of the shaft, a mirror center, which is defined as a point on the reflective surface closest to the center axis of the shaft, is aligned with the light beam center when the mirror is at the first position, and the mirror center shifts within the motion area when the mirror is swinging between the first position, non-inclusive, and the second position, inclusive, the reflective surface has a pair of edge portions that are opposite to each other in a width direction of the mirror, the first light beam and the second light beam are reflected by the pair of edge portions when the mirror is at the first position, the light source includes two light emitting elements that collectively emit the light beam, the reflective surface has a rectangular shape and includes a center portion including the mirror center and the pair of edge portions extending in a direction along the center axis, and the light beam from the two light emitting elements is reflected by the mirror at the center portion when the mirror is at the second position.
 2. The LIDAR device according to claim 1, wherein the mirror center is a center between the pair of edge portions.
 3. The LIDAR device according to claim 1, further comprising a controller configured to control the motor to swing the mirror between the first position and the second position.
 4. The LIDAR device according to claim 1, wherein the rotatable shaft has a columnar shape and includes a side surface that is connected to the back surface of the mirror. 